New York mulls sea walls to hold back future surges

Arriving in Venice years ago, Robert Benchley, the New York journalist and wit, is said to have sent a mock-panicked telegram to his editor: "Streets flooded. Please advise."

After the enormous storm last week, which genuinely panicked New York with its staggering and often fatal violence, residents here could certainly identify with the first line of Benchley's note. But what about the second?

A family is rescued from the Dongan Hills neighborhood in the Staten Island borough of New York. Photo: New York Times

If, as climate experts say, sea levels in the region have not only gradually increased, but are also likely to get higher as time goes by, then the question is: What is the way forward? Does the city continue to build ever-sturdier and ever-higher sea walls? Or does it accept the uncomfortable idea that parts of New York will occasionally flood and that the smarter method is to make the local infrastructure more elastic and better able to recover?

Gov. Andrew M. Cuomo on Wednesday gave a sea wall the nod. Because of the recent history of powerful storms hitting the area, he said, elected officials have a responsibility to consider new and innovative plans to prevent similar damage in the future.

"Climate change is a reality," Cuomo said. "Given the frequency of these extreme weather situations we have had, for us to sit here today and say this is once in a generation and it's not going to happen again, I think would be shortsighted."

But some experts in the field who have thought deeply about how to protect New York from huge storms like Hurricane Sandy — and especially from the coastal surges they produce — suggested that less intrusive forms of so-called soft infrastructure might prove more effective in sheltering the city than mammoth Venetian sea walls. Mayor Michael R. Bloomberg seemed to agree with them on Thursday when he said: "I don't think there's any practical way to build barriers in the oceans. Even if you spent a fortune, it's not clear to me that you would get much value for it."

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According to the experts — architects, environmentalists and civil engineers — large-scale projects like underwater gates are expensive, cumbersome and difficult to build. More important, they say, such undertakings are binary projects that work just fine until the moment they do not.

Whatever the way forward, Klaus H. Jacob, a Columbia University seismologist and an expert on urban environmental disasters, said the century-event of Hurricane Sandy could become, because of rising seas alone, an annual occurrence by 2100.

"We know what we have to do," said Jacob, who predicted last week's tragedy with eerily prescient detail in a 2011 report. "The question is when do we get beyond talking and get to action."

Among those actions already proposed are relatively minor alterations to the building code, to ban housing boilers and electrical systems in basements, and slightly more apocalyptic strategies, like one known as managed retreat, in which people would cede low-lying areas to the sea. While no one is calling for a mass and permanent exodus from the Rockaways, for instance, some experts, like Radley Horton, a climatologist at Columbia University, said that as parts of New York became more difficult — and costly — to protect, managed retreat needed at least to become "part of the public discussion."

Here, then, are three proposals — some traditional, some fantastic, but all at least theoretically workable — designed to reduce the effects of storms like Hurricane Sandy on three especially vulnerable New York neighborhoods: Lower Manhattan, the Red Hook and Gowanus sections of Brooklyn, and the northern shore of Staten Island.

Picture a fringe of mossy wetlands strapped like a beard to Lower Manhattan's chin, and you are halfway toward imagining the plan to protect the financial district and its environs dreamed up by the architect Stephen Cassell and a team from his firm, Architecture Research Office, and a partner firm, dlandstudio.

"Our goal was to design a more resilient city," Cassell said. "We may not always be able to keep the water out, so we wanted to improve the edges and the streets of the city to deal with flooding in a more robust way."

Among the most disturbing images to emerge from the aftermath of the storm was that of a pile of cars floating upended in the waters of a parking lot near Wall Street. Lower Manhattan, where most of the borough's power failures occurred, is vulnerable to floods like this not just because it sits low in relation to the sea; it also juts out on heaps of artificial landfill, into the fickle waters of New York Harbor. It is probably not coincidental that the flooded areas of Manhattan, largely correspond to the island's prelandfill borders.

To prevent incursions by water, Cassell and his planners imagined ringing Lower Manhattan with a grassy network of land-based parks accompanied by watery patches of wetlands and tidal salt marshes. At Battery Park, for instance, the marshes would weave through a series of breakwater islands made of geo-textile tubes and covered with marine plantings. On the Lower East Side of the island, Cassell and his team envisioned extending Manhattan by a block or two — with additional landfill — to create space for another new park and a salt marsh.

Beyond serving as recreation areas, these engineered green spaces would sop up and reduce the force of incoming water.

"When there's a storm surge, it creates an enormous amount of energy," Cassell said. "Wetlands absorb that energy and protect the coastline."

As a complement to the parks and marshes, Cassell's team would re-engineer the streets in the neighborhood to make the area better able to handle surging waves, creating three variations of roadway. On so-called Level 1 streets, asphalt would be replaced with absorptive materials, like porous concrete, to soak up excess water like a sponge and to irrigate plantings in the street bed. Level 2 streets, planned for stronger surges, would send running water into the marshes at the island's edges and also into prepositioned ponds meant to collect runoff for dry spells. Level 3 streets — the only ones that might require a shift in the current city grid — would be parallel to the shoreline and designed to drain surging water back into the harbor.

"We weren't fully going back to nature with our plan," Cassell said. "We thought of it more as engineered ecology. But if you look at the history of Manhattan, we have pushed nature off the island and replaced it with man-made infrastructure. What we can do is start to reintegrate things and make the city more durable."

Staten Island: a bridge in troubled waters

A few years ago, Lawrence J. Murphy, an engineer in the New York office of the global engineering firm CDM Smith, was asked by the local chapter of the American Society of Civil Engineers to propose a way of protecting northern Staten Island from the forces of a Category 3 hurricane. He came up with a plan to build a classic storm-surge barrier across the Arthur Kill, the tidal strait that separates Staten Island from the mainland of New Jersey, designed to act in concert with similar barriers in the East River, the Narrows and the waters near the Rockaway Peninsula.

Staten Island was ravaged by Hurricane Sandy, as entire neighborhoods were flooded, a 168-foot water tanker crashed onshore and city officials said that most of the fatalities in the city occurred there. It is arguably New York's most exposed borough, surrounded not by peaceful rivers but by oceanic channels like the Arthur Kill and, of course, the Atlantic itself.

Murphy's concept, created with his partner, Thomas Schoettle, calls for the construction of a damlike structure with suspension towers spanning the Arthur Kill. Tidal gates below the surface would open and close as needed.

According to the Army Corps of Engineers, Category 3 hurricanes (Hurricane Sandy was a Category 1 storm, downgraded by the time it reached New York) would produce surges of slightly more than 14 feet above normal sea levels. Murphy designed his barrier to protect against "overtopping waves" of an additional 8 feet, for a total height of 22 feet. He also designed a complex system of locks and drawbridges to accommodate the numerous commercial ships that navigate the kill.

Murphy's barrier would be run by a trained staff and would operate on emergency power in the event of an electrical failure. Because strong tides pass through the kill, he would also outfit the barrier with tidal generators, which, as an extra benefit, could produce electricity.

Nor did Murphy ignore the possibilities of public recreation.

"The concept design of the Arthur Kill Storm Barrier has been made with a focus on aesthetics to create a destination," he wrote in his proposal. "The multiuse path can provide bicycling and walking opportunities. Fishing and bird-watching amenities can also be provided."

Red hook and gowanus: Oysters to the rescue

The architect and landscape designer Kate Orff based her plan to shield the Red Hook and Gowanus neighborhoods of Brooklyn on the outsize powers of the oyster.

"The era of big infrastructure is over," Orff said. By placing her faith in a palm-size bivalve to reduce the effects of surging storms, Orff said, she is "blending urbanism and ecology" and also "looking to the past to reimagine the future."

Red Hook, in particular, was thrashed by Hurricane Sandy as some of the local inlets, like the Buttermilk Channel and Gowanus Bay, spilled into the low-lying area, swamping public housing projects and sending water rushing so high through the streets it occasionally swallowed up cars and bicycles.

Orff's proposal, created by a team at her design firm Scape/Landscape Architecture PLLC, envisions a system of artificial reefs in the channel and the bay built out of rocks, shells and fuzzy rope that is intended to nurture the growth of oysters (she calls them "nature's wave attenuators").

The Bay Ridge Flats, a stretch of water that sits off the coast of the Brooklyn Army Terminal, was once home to a small archipelago of islands that protected the Brooklyn coastline. The islands have long since disappeared because of dredging, and Orff would replace them with her oyster-studded barriers, which, over time, would form a sort of "ecological glue" and mitigate onrushing tides, she said.

At the same time, she imagines installing oyster beds along the banks of the Gowanus Canal in a series of Floating Upweller Systems (Flupsys) — essentially, artificial shellfish nurseries. A powerful fan blows aerated water through a group of eight chambers in which oysters or mussels can be grown. The chambers protect the budding oysters from predators like starfish. Above the Flupsys, Orff would place a public walkway for joggers and strollers, punctured every so often by hatches that could be lifted to permit a view of the nature below.

"This is infrastructure that we can do now," she explained. "It's not something we have to think about and fund with billions of dollars 50 years down the road."

Oysters have the added benefit of acting as natural water filters — a single one can clean up to 50 gallons of water a day. By being placed in the Gowanus Canal, Orff hopes, they could further purify what has already been named a federal Superfund site. She wants, by way of her project, to change how we think about infrastructure projects.

"Infrastructure isn't separate from us, or it shouldn't be," Orff said. "It's among us, it's next to us, embedded in our cities and our public spaces."